Ecosystem ecology studies the flow of energy and materials through organisms and the physical

environment as an integrated system.

a population

reproductionthrough generations

resources

?

Ecosystem ecology divides the world into pools and fluxes of materials and energy:

N

N N

N

N

N

NNN N

N

NN

N

N

Pools are quantities of materials such as carbon & nitrogen, that are contained in certain subdivisions of the ecosystem.

They are measured in g or moles per m2.

Pool of all forms of N in living plant

biomass

Pool of inorganic N in the soil (NO3

and NH4).

N

Fluxes are rates of material transfer between pools, measured in g or

moles per m2 per day or year.

water vapor release

More live biomass

litter

O2 release

CO2 uptake

Absorbs light

Water uptake

Soil nutrient uptake:

N,P,S,K,…

root exudates (complex sugars, allelochemicals?,

leached N

Matter fluxes through a typical primary producer:

Matter fluxes through a typical primary consumer:

C, N, H2O, etc. in dung

C, N, H2O, etc. in milk

C, N, H2O, etc. in grass

C, N, H2O, etc. in the dead cow

C, N, H2O, etc. in a calf

C, N, H2O, etc. in urine

O2 of air intake

CO2 of air expelled

Methane, CO2

Scavengers: vertebrate carrion eaters,Seldom restricted to carrion.

Detritivores: invertebrate consumers of organic matter.

Decomposers: fungi and bacteria.

Matter fluxes through a decomposer, detritivore, or scavenger:

More decomposers, detritivores or scavangers

simpler organic waste

CO2 release

O2 uptake

C, N, H2O, etc in dead organic matter

C, N, H2O, etc. in the dead decomposer

Dead organic matter from

carrion, litter,

feces & urine

Net primary production:(the biomass produced by autotrophs)

Herbivores(primary consumers)

Scavengers,Detritivores &Decomposers

(primary consumers)

Carnivores I(secondary consumers)

Carnivores I(secondary consumers)

Carnivores II(tertiary consumers)

Carnivores II(tertiary consumers)

Generalized trophic web

is eaten by adds

Questions we can address only through ecosystem ecology:

“Budget questions” (How do all the fluxes and the changes in

pool size add up?)

• What happens to the portion of the nitrogen that is added to the

farmers field but is not harvested with the crop?

• What is the fate of CO2 expelled to the atmosphere from burning

fossil fuels?

• How much of the annual rainfall is returned to the atmosphere

via plant transpiration, soil evaporation, and how much goes to

groundwater?

“Comparative questions” (Why do ecosystems differ in pool sizes and

fluxes? What are the controls over ecosystem processes?)

• Why do ecosystems differ in the %carbon that sits in living

plants versus in the soil organic matter? (E.g. : tropical forests =

most carbon in biomass, tundra = most carbon in soil.)

• How does plant species composition and diversity affect the

productivity of grasslands and forests?

• How will climate change (=warmer temperatures, different

precipitation patterns) affect productivity and species diversity?

Questions we can address only through ecosystem ecology:

Climate Vegetation Feedbacks:

VegetationVegetation

amount and compositionamount and composition

Local weatherLocal weather

patternspatterns

Earth’s climate systemEarth’s climate system

Land Land managementmanagement

Changes in Changes in atmospheric atmospheric compositioncomposition

Energy and material cycles:

Solar energy drives:

• The hydrologic cycle

• The carbon cycle

• The nitrogen and most other mineral cycles

Earth Energy Balance

Hydrologic cycle

The Nitrogen Cycle

Carbon cycle

Global carbon pools and residence times

Photosynthesis:The rate of carbon assimilation per area of photosynthetic area.

6H2O + 6CO2 + light ----------> C6H12O6+ 6O2

respiration

O2 CO2

root exudates

new biomass

The rate of plant

respiration per unit area (Rp)

The rate of carbon fixation per unit area:

Gross Primary Production

(GPP) Net Primary Production

into the trophic web

Net Primary Production (NPP)

Net carbon gain in biomass(= total carbon absorbed by plants (GPP) – carbon released by

plant respiration Rp)

NPP is primarily controlled by precipitation and temperature:

DESRT: desertTUNDR: tundraWDLND: woodlandBOENL: boreal evergreen,

needle-leafedBODBL: boreal decciduous,

broad-leafedBODNL: boreal deciduous, needle-leafedGRSTE: temperate grasslandGRSTR: tropical grasslandTEDBL: temperate deciduous

broad-leafedTEENL: temperate evergreen,

needle-leafedTEEBL: temperate evergreen,

broad-leafedTRDBL: tropical deciduous,

broad-leafedTREBL: tropical evergreen,

broad-leafed

The major earth biomes differ in NPP with precipitation. A

bove

-gro

und

NP

P g

m-2 y

r-1

Global distribution of primary productivity

Net Ecosystem Exchange (NEE)

= Carbon absorbed or released by the entire ecosystem(GPP – ecosystem respiration)

The rate of ecosystem respiration (RP+Rs)

The rate of carbon/energy fixation: Gross

Primary Productivity

(GPP) Net Ecosystem Exchange

This is the carbon that stays in the

ecosystem.

The rate of ecosystem respiration (RP+Rs)

The rate of carbon/energy fixation: Gross

Primary Productivity

(GPP) Net Ecosystem Exchange

This is the carbon that comes out of the ecosystem.

Net Ecosystem Exchange (NEE)

= Carbon absorbed or released by the entire ecosystem(GPP – ecosystem respiration)

Carbon Sequestration:

The long-term storage of carbon in the terrestrial biosphere or the oceans, thus removing CO2 from the atmosphere.

(Negative fluxes indicate net CO2 uptake by the ecosystem)Data courtesy of Jim Heilman, Texas A&M and Marcy Litvak, University of New Mexico.

Net Ecosystem Exchange at Freeman Ranch

Net Ecosystem Exchange at Freeman Ranch

Grassland site

Woodland site

Transition site

(Freeman Ranch is taking up carbon)Data courtesy of Jim Heilman, Texas A&M and Marcy Litvak, University of New Mexico.

Cumulative ecosystem carbon gain